CN1985311A - Focus control in a multiple-beam disc drive - Google Patents

Focus control in a multiple-beam disc drive Download PDF

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Publication number
CN1985311A
CN1985311A CNA2005800238343A CN200580023834A CN1985311A CN 1985311 A CN1985311 A CN 1985311A CN A2005800238343 A CNA2005800238343 A CN A2005800238343A CN 200580023834 A CN200580023834 A CN 200580023834A CN 1985311 A CN1985311 A CN 1985311A
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China
Prior art keywords
opt
optimum
numbering
detector
adjustable element
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CNA2005800238343A
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Chinese (zh)
Inventor
T·W·图克
C·T·H·F·利登鲍姆
A·M·范德利
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Koninklijke Philips NV
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Koninklijke Philips Electronics NV
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Publication of CN1985311A publication Critical patent/CN1985311A/en
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    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/13—Optical detectors therefor
    • G11B7/131—Arrangement of detectors in a multiple array
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B7/0908—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for focusing only
    • G11B7/0917—Focus-error methods other than those covered by G11B7/0909 - G11B7/0916
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B7/0943—Methods and circuits for performing mathematical operations on individual detector segment outputs
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/14—Heads, e.g. forming of the optical beam spot or modulation of the optical beam specially adapted to record on, or to reproduce from, more than one track simultaneously

Abstract

A method for controlling an optical disc drive apparatus (1) which comprises: light beam generating means (31) for generating a plurality of N optical beams (32(i)); means (33, 34, 37) for focussing said beams in respective focus spots (F(i)); at least one adjustable member (34) for axially displacing said focus spots; comprises the step of calculating an optimum setting <SUB>(ZOPTIMUM) </SUB>for the adjustable member (34), such that the out-of-focus condition for the optical system (30) as a whole is as small as possible. The position of the adjustable member (34) may be controlled to be substantially equal to the said optimum setting (Z<SUB>OPTIMUM</SUB>). Or, one specific beam is maintained in a focus condition, the beam having number <SUB>m=mOPT </SUB>selected according to m<SUB>OPT</SUB> =+- INTEGERSQUARE{(N-1)/(2v2 in case N is odd or mOPT = +- INTEGERROUND IN-(N-2)/8) in case N is even.

Description

Focus control in multiple-beam disc drive
Technical field
The present invention relates to optical recording and light is read the field.More specifically, the present invention relates to/write/read the field of information from optical storage media.A kind of known optical storage media is an optical memory disc; Therefore, will explain the present invention, but should notice clearly that because the present invention can also be applied to the optical storage media of other types, therefore described explanation is not interpreted as and limits the scope of the invention in conjunction with optical memory disc.
Background technology
As known to those skilled in the art, optical memory disc comprises with the form of the data pattern storage space of canned data thereon.CD can be read-only type, and information writes down during manufacture in this dish, and described information can only be read by the user.But optical memory disc can also be an once-type, can come canned data by the user in this dish.
For information being write in the storage space of optical memory disc, perhaps in order to read information from described dish, disc drive apparatus (hereinafter also being referred to as " CD drive ") comprises on the one hand the whirligig that is used to receive with rotary CD, also comprises the optical scanner that is used to produce light beam (typically being laser beam) and is used to use the described storage space of described laser beam flying on the other hand.Because the technology of optical discs in general, can be in CD canned data method and can be known from the method for CD reading optical data, so do not need to illustrate in further detail this technology herein.
Described light scanning apparatus comprises beam generated device (being generally laser diode), be used to receive from the light of dish reflection and be used to produce the photodetector output signal fluorescence detector, be used for light from the device of generation device positioning disk be used for the device of the guides reflected light detecting device that obtains from dish.Data pattern by dish is modulated described reflected light, and described modulation conversion becomes the modulation of photodetector output signal.
During operation, light beam should keep being focused on the dish.For this reason, object lens are arranged to that axially-displaceable puts, and CD drive comprises the actuator means of the axial location that is used to control object lens.
Such system is arranged, and light scanning apparatus includes only a laser beam in this system, and it is at dish on focal beam spot of projection.An embodiment of this system is represented as the 1D system: or with the form of continuous helical, or with a plurality of concentrically ringed forms, data are arranged to the linear dot pattern that is expressed as track.The 1D dish can have a plurality of tracks.In such system, have only a laser beam to be focused, and for the focused condition of this laser beam of optimization, described actuator means only need the axial location of optimization object lens.
Yet, also there are many spot system, promptly produce the system of a plurality of light beams that throw a plurality of focal beam spots simultaneously therein.An example of this system is represented as the 2D system: data are read out by a plurality of hot spots with the 2D structural arrangement.A plurality of tracks that also may be the 1D dish are read by a plurality of hot spots simultaneously.Typically, these many hot spots are located substantially on the straight line, and this straight line and hot spot dislocation direction (or better: medium dislocation direction is a tangential direction under the situation of dish promptly) are at an angle.
For each hot spot of this many spot system, wish that hot spot can accurately be focused on the storage space of dish.Yet, for example because the plane of CD is not flat fully such fact generally, perhaps for example because object lens have field curvature so that the multiple beam hot spot can not be accurately positioned such fact in the plane, the burnt condition of this poly is difficult to reach, and perhaps this focused condition may be impossible.In addition, the axial location of regulating a plurality of focal beam spots individually is impossible: only may side by side move axially all focal beam spots.In fact, this means and have only one or two laser beam will be in the vernier focusing condition at most, and other light beam is in unfocused state on little or big degree.
Therefore, a target of the present invention is to find the solution of the problems referred to above.
Summary of the invention
According to a first aspect of the invention, object lens are set at best axial location, calculate this best axial location so that generally for the non-focusing condition (out-of-focuscondition) of system, promptly consider together all light beams the non-focusing condition as far as possible little.
According to a second aspect of the invention, utilize a particular beam of selecting to carry out focus control, for the non-focusing condition of system, promptly consider all light beams together on the whole so that when this particular beam is in accurate focused condition, all as far as possible little.
Description of drawings
Above-mentioned and other aspects of the present invention, feature and advantage will further obtain explaining that wherein identical reference number is indicated same or analogous parts by following description with reference to accompanying drawing, and wherein:
Fig. 1 schematically represents the associated components of disc drive unit;
Fig. 2 A represents a plurality of independent light beams;
Fig. 2 B is the top schematic view of a part of accumulation layer of an embodiment of 2D code-wheel;
Fig. 2 C represents to be positioned at a plurality of independent focal beam spot on the crooked focussing plane;
The expression of Fig. 3 A and Fig. 3 B signal is respectively for the relative positioning of a plurality of hot spots of odd number hot spot and even number hot spot;
The expression of Fig. 4 A and Fig. 4 B signal is respectively for two systems to the hot spot numbering of being used for of odd number hot spot and even number hot spot;
Fig. 5 A and Fig. 5 B are the tables of representing respectively for odd number hot spot and even number hot spot as the m optimum value of the function of N;
Fig. 6 is the diagrammatic sketch of schematically representing according to the preferred details of optical system of the present invention.
Embodiment
Fig. 1 schematically represents to be applicable at CD 2 (being typically DVD or CD) and goes up canned data and read the disc drive unit 1 of information from it.The dish 2 that its thickness is shown in the amplification mode has at least one accumulation layer 2A.For rotating disc 2, disc driving equipment 1 comprises a motor 4 that is fixed on the framework (for the sake of clarity and not illustrating), and it has defined a turning axle 5.
Disc driving equipment 1 also comprises an optical system 30 by beam flying dish 2.More concrete, in exemplary configurations shown in Figure 1, optical system 30 comprises a beam generated device 31, is generally laser instrument, laser diode for example, and it is arranged to produce light beam 32.Below, follow the different piece of the light beam 32 of light path 39 and represent waiting for character a, b, the c of reference number 32 by interpolation.
Light beam 32 is through beam splitter 33, collimation lens 37 and object lens 34 (light beam 32b) arrival dish 2.Light beam 32b is from coiling 2 reflections (folded light beam 32c) and arriving photodetector 35 through object lens 34, collimation lens 37 and beam splitter 33 (light beam 32d).Object lens 34 are designed on accumulation layer 2A light beam 32b to be focused into focal beam spot F.
Disc driving equipment 1 also comprises an actuator system 50, and it comprises the radial actuator 51 for dish 2 radially mobile object lens 34.Because radial actuator itself is known, and the present invention does not relate to the Design and Features of described radial actuator, therefore do not need at length to discuss the Design and Features of radial actuator here.
In order to reach and to keep correct focused condition, described object lens 34 are installed by axially-displaceable with putting, and actuator system 50 also comprises for the dish 2 axial focus actuator 52 that go up dislocation object lens 34 and arrange in addition simultaneously.Because focus actuator itself is known, and the design of further this focus actuator is not theme of the present invention with operation, therefore do not need at length to discuss the design and the operation of this focus actuator here.
In order to reach and keep the correct obliquity of object lens 34, object lens 34 can be installed with being tilted; In this case, as directed, actuator system 50 also comprises the tilt actuators 53 of arranging for dish 2 pitching object lens 34.Because tilt actuators itself is known, and the design of further this tilt actuators and operation be not theme of the present invention, therefore do not need at length to discuss the design and the operation of this tilt actuators here.
Should note being used for relative device frame in addition supports the device of object lens and is used for axially and radially the device of dislocation object lens and the device itself that is used for the pitching object lens all are known.Because the design of this support and displacement and operation are not themes of the present invention, therefore do not need at length to discuss their design and operation here.
Should notice that in addition radial actuator 51, focus actuator 52 and tilt actuators 53 may be implemented as the actuator of an integral body.
Disc driving equipment 1 also comprises a control circuit 90, its have the control input end of radial actuator of being coupled to 51 first output terminal 91, have the control input end of focus actuator of being coupled to 52 second output terminal 92, have the 3rd output terminal 93 of the control input end of tilt actuators of being coupled to 53, the 5th output terminal 96 that has the 4th output terminal 94 of the control input end of being coupled to motor 4 and have the control input end of being coupled to laser equipment 31.Control circuit 90 is designed to produce the control signal S that is used to control radial actuator 51 at its first output terminal 91 CR, producing the control signal S that is used to control focus actuator 52 at its second output terminal 92 CF, produce the control signal S that is used to control tilt actuators 53 at its 3rd output terminal 93 CT, produce the control signal S that is used to control motor 4 at its 4th output terminal 94 CMAnd the control signal S that is used to control laser in its 5th output terminal 96 generations W
Control circuit 90 also has one and is used for receiving read signal S from photodetector 35 RRead signal input end 95.In fact photodetector 35 can comprise a plurality of independent detecting elements (itself being known), and read signal S RIn fact can form by a plurality of independent detecting element output signals (itself also being known).In addition, in fact read signal input end 95 can comprise the input signal terminal that several are independent, and each input signal terminal receives a relevant detection device element output signal, and this itself also is known.
Control circuit 90 is designed to handle independent detecting element output signal to obtain one or more error signals.Radial error signal or tracking error signal (being designated hereinafter simply as TES) are illustrated in the radial distance between tracking and the focal beam spot F.Focus error signal (being designated hereinafter simply as FES) is illustrated in the axial distance between accumulation layer and the focal beam spot F.Attention can be used different formula according to the design of photodetector for error signal calculation.
Under reading mode, the intensity of laser beam 32 is retained as substantially constant, and the data content of the track that is being read of the variation of the intensity of the independent detecting element output signal that receives at read signal input end 91 reflection.Control circuit 90 also comprises a data input end 97.In WriteMode, control circuit 90 is based on the data-signal S that receives at its data input pin 97 DATAGeneration is used for laser 31 control signal S W, make laser beam intensity fluctuates be used to write and import the corresponding pattern of data.Different strength grades also is used to wipe rewritable disk, and described erase process can be when rewriteeing available data or carries out as the individual processing of the dish that soars.
Though Fig. 1 and above-mentioned general description are all effective basically for a spot system and many spot system, Fig. 2 A-C represents some concrete aspect of many spot system.Fig. 2 A be with reference to Fig. 1 with the view of vast scale more, in fact its expression light beam 32 comprises a plurality of independent light beams, is typically expressed as 32 (i).In Fig. 2 A, four independent light beams 32 (1), 32 (2), 32 (3), 32 (4) have only been shown.
Fig. 2 A represents that each independent light beam 32 (i) is focused on the corresponding independent focal beam spot F (i), and each independent beam reflected 32 (i) is received by corresponding photodetector 35 (i).
Fig. 2 B is the schematic top view of a part of accumulation layer of the example of 2D code-wheel, its expression is with two-dimensional data array DA (being hexagonal array in this embodiment) array data pit DP, described two-dimensional data array DA definition is by the broad gauge mark of a plurality of focal beam spot scannings, and 11 focal beam spots are represented as the black spots of adularescent numeral thereon in this embodiment.A plurality of focal beam spots are positioned on vertically (in the drawings for from accomplishing right direction) line at an angle with track, and hot spot spacing and described angle are set to make this group hot spot and cross over whole track.
Fig. 2 C is with reference to the view of Fig. 2 A with bigger ratio, and it illustrates the xsect of the part of dish 2, represents that in exaggerative mode independent focal beam spot F (i) is positioned at crooked focussing plane FP.Because axially (focus actuator 52) mobile optical lens 34 will move axially all focal beam spot F (i) of all independent light beams 32 (i), therefore wish to organize the actual disposition of independent focal beam spot F (i) according to this, one or two that has only those independent focal beam spot F (i) correctly located, promptly consistent with accumulation layer 2A, it keeps accurately for focal beam spot F (3) and F (7) in diagram.Every other hot spot is positioned on the axial distance of accumulation layer 2A.
Should be understood that this situation causes the problem that data are read: the axial distance between focal beam spot and the accumulation layer is big more, and corresponding photodetector can not produce corresponding to the chance of the correct data read output signal of the data pits that is scanned by this focal beam spot just big more.
Below, the axial location of object lens 34 will be represented as Z (lens), and the axial distance between the ideal position of the physical location of i focal beam spot F (i) and i focal beam spot F (i) (promptly and accumulation layer 2A consistent) will be represented as Δ z (i).
According to a first aspect of the invention, it is as well as possible that the axial location Z (lens) of object lens 34 is set to make the global focusing condition of a plurality of light beams.This position of object lens 34 will be represented as best axial lens position Z OPTIMUM, and corresponding global focusing condition will be represented as the optimal accumulated condition.Therefore, we can say for following formula optical system 30 and meet the optimum focusing condition:
Z(lens)＝Z OPTIMUM (1)
According to another aspect of the present invention, (be expressed as MAX (Δ z (i)) and hour obtain the optimum focusing condition as far as possible when the maximal value of all distance, delta z (i).
Fig. 3 A represents that the sum for light beam equals an aspect of the situation of odd number (promptly 3,5,7...), equals an aspect of the situation of even number (promptly 2,4,6...) and Fig. 3 B represents sum for light beam.Below, suppose that a plurality of focal beam spot F (i) are arranged according to the pattern of symmetry.
In Fig. 3 A and 3B, Z-axis is represented the axial location z along primary optical axis, and transverse axis be illustrated between the hot spot measured on the direction perpendicular to optical axis and the primary optical axis apart from x.Suppose for all hot spots all equating between sequential focusing hot spot F (i) and F (i+1) apart from x.
Under the situation of odd number hot spot (Fig. 3 A), center spot F (C) is positioned at (x=0) on the z axle, and equals F (O)=(N-1) d/2 apart from x between center spot F (C) and the outer spots F (O).
Under the situation of even number hot spot (Fig. 3 B), two interior side spots F (I) are positioned at the both sides of z axle with distance x=d/2, and two outer spots are positioned at the both sides of z axle with distance x=(N-1) d/2.
In first is similar to, approaches the curvature of the focussing plane FP of optical axis and can describe by following formula:
(z-z 0)＝-x 2/(2R) (2)
Z wherein 0The position z of the intersection point of expression focussing plane FP and optical axis (promptly at x=0);
And wherein R represents the radius of focussing plane FP.
Under the situation of odd number hot spot (Fig. 3 A), center spot F (C) is positioned at:
z(C)＝z 0， (3)
And outer spots F (O) is positioned at:
z(O)＝z 0-[(N-1)·d/2] 2/(2R). (4)
Therefore, the axial distance between center spot F (C) and the outer spots F (O) equals (N-1) 2D 2/ (8R).Can easily find out best axial lens position Z OPTIMUMSatisfy formula:
Z OPTIMUM-z 0＝-(N-1) 2·d 2/(16R) (5)
Wherein MAX (Δ z (i)) reaches its minimum value:
MAX(Δz(i)) MIN＝(N-1) 2·d 2/(16R) (6)
Under the situation of even number hot spot (Fig. 3 B), interior side spots F (I) is positioned at:
z(I)＝z 0-[d/2] 2/(2R)， (7)
And outer spots F (O) is positioned at:
z(O)＝z 0-[(N-1)·d/2] 2/(2R). (8)
Therefore, the axial distance between interior side spots F (I) and the outer spots F (O) equals N (N-2) d 2/ (8R).Can easily find out best axial lens position Z OPTIMUMSatisfy formula:
Z OPTIMUM-z 0＝-(N 2-2N+2)·d 2/(16R) (9)
Wherein MAX (Δ z (i)) reaches its minimum value:
MAX(Δz(i)) MIN＝N·(N-2)·d 2/(16R) (10)
Though the best solution for control circuit 90 is a driving axial actuator 52 so that keep lens position Z (lens) to equal best axial lens position Z according to formula (5) or (9) in theory OPTIMUM, but be difficult in practice realize, this be since in this case in a plurality of probably light beams neither one in fact focus on the accumulation layer 2A, this makes and is difficult to obtain reliable focus error signal.In preferred axially control system, control circuit 90 is designed to driving axial actuator 52 so that at least one independent focal beam spot is consistent with accumulation layer 2A.Therefore,, a specific focal beam spot is selected in focus control, just be used to make z (i)-Z in order to depart from the best in theory solution of above-mentioned definition as small as possible OPTIMUMThe as far as possible little specific focal beam spot F (i) of difference.
Below, light beam will be numbered according to different systems with focal beam spot, as making an explanation with reference to figure 4A and 4B.
Be numbered as 1,2,3,4 ... N-1, under the situation of the odd number focal beam spot F (i) of N, center spot F (C) will have numbering (N+1)/2.In the new numbering shown in Fig. 4 A, center spot F (C) will obtain numbering m=0, and its adjacent hot spot will obtain numbering m=1 and m=-1 or the like, and outer spots F (O) will have numbering m=(N-1)/2 and m=-(N-1)/2.Therefore, equal md apart from x between hot spot m and the optical axis.About the axial location of hot spot m, the formula below being suitable for:
(z(m)-z 0)＝-[m·d] 2/(2R) (11)
Above-mentioned formula is combined best as can be seen axial lens position Z with formula (5) OPTIMUMAnd the axial distance between the axial location of hot spot m can be expressed as:
z(m)-Z OPTIMUM＝(N-1) 2·d 2/(16R)-[m·d] 2/(2R) (12)
For optimal spot, the value of formula (12) expression should be as far as possible little.In ideal conditions, this value equals zero.Can be readily seen that, in the ideal case, be suitable for m=(N-1)/(2 √ 2), but this is not a round values.
Therefore, according to the present invention, select optimal spot numbering m OPTSo that the absolute value of formula (12) expression is as far as possible little or simplify so that:
| m OPT 2 - ( N - 1 ) 2 8 | As far as possible little.
Below, defined function y=INTEGERSQUARE{x}, wherein y is its square y 2Near x 2Integer.
Therefore, above-mentioned requirements satisfies:
m OPT＝±INTEGERSQUARE{(N-1)/(2√2)} (13)
The optimum value of noting m does not rely on d, and does not rely on R; The optimum value of m only depends on N.Therefore, can obtain showing the table of the optimum value of m as the function of N.The table that Fig. 5 A comes to this, expression is for a lot of value N (N-1) 2/ 8 and m OPTThis table is also represented m OPT 2Attention has been omitted in this table ± possibility.
Attention is unworthy under the situation of N=1; In fact, this even is not the situation of a plurality of light beams.
It shall yet further be noted that under the situation of N=3 answer m OPT=1 (or-1) causes center spot F (2) to equal away from the axial distance of accumulation layer | z (2)-z (1) |.Alternatively, answer m OPT=0 can cause outer spots F (1) and F (3) to have above-mentioned distance apart from accumulation layer.Therefore, the non-focusing condition of above-mentioned definition is for m OPT=0 and m OPT=1 answer all is the same.
Similarly, under the situation of N=11, m OPT=3 and m OPT=4 all is best.
Shown in Fig. 4 B, be numbered 1,2,3,4, ... N-1, under the situation of the even number focal beam spot F (i) of N, interior side spots F (I) will obtain numbering m=1 and m=-1, their adjacent hot spots will obtain numbering m=2 and m=-2 or the like, and outer spots F (O) will obtain numbering m=N/2 and m=-N/2.Therefore, the distance of the x between hot spot m and the optical axis equals (2m-1) d/2.About the axial location of hot spot m, the formula below being suitable for
(z(m)-z 0)＝-[(2m-1)·d/2] 2/(2R) (14)
Above-mentioned formula is combined best as can be seen axial lens position Z with formula (9) OPTIMUMAnd the axial distance between the axial location of hot spot m can be expressed as:
z(m)-Z OPTIMUM＝(N 2-2N+2)·d 2/(16R)-[(2m-1)·d/2] 2/(2R) (15)
For optimal spot, the value of formula (15) expression should be as far as possible little.In the ideal case, this value equals zero.Can easily find out, in the ideal case, make 4m=2+ √ (2N 2-4N+4), but m is not integer usually.
It can also be seen that from formula (15), for optimal spot ideally, be suitable for m (m-1)=N (N-2)/8.
Therefore, according to the present invention, select optimal spot m OPTSo that the as far as possible little or simplification of the absolute value of formula (15) expression, so that:
| m OPT ( m OPT - 1 ) - N ( N - 2 ) 8 | As far as possible little.
Below, defined function z=INTEGERROUND{x}, wherein z makes z (z-1) near the integer of x.
Therefore, above-mentioned requirements satisfies:
m OPT＝±INTEGERROUND{N·(N-2)/8} (16)
In addition, the optimum value of m only depends on N.Fig. 5 B is N (N-2)/8 and the m of expression for a lot of value N OPTTable.This table is also represented m OPT(m OPT-1).Attention has been omitted in this table ± possibility.
The situation of noting N=2 is valueless.
Should also be noted that under the situation of N=4 answer m OPTSide spots F (2) and F (3) equaled from the axial distance of accumulation layer in=2 (or-2) caused | z (2)-z (1) |.Alternatively, answer m OPT=1 (or-1) can cause outer spots F (1) and F (4) to have above-mentioned distance from accumulation layer.Therefore, non-focusing condition defined above is to answer m OPT=1 and m OPT=2 all is the same.
Similarly, under the situation of N=18, m OPT=6 and m OPT=7 all is best.
Fig. 6 represents to be applicable to the details of the embodiment of the photodetector 35 in the multiple beam optical system.Multiple beam photodetector 35 comprises a plurality of detector cells 35 (i), between them by arrangement adjacent one another are so that can receive beam reflected 32d (i) respectively.If N represents the numbering of light beam 32i, then the quantity of detector cell 35 (i) should equal N at least.
The example of Fig. 6 represents to have the multiple beam optical system of 11 light beam 32i.Each detecting device is represented as a square, places reference number 35 (1) above it, and 35 (2) ... 35 (11).Certainly, the photosensitive surface of photodetector unit 35 (i) in fact can be a square, but this is inessential, and therefore illustrated square does not mean that restriction scope required for protection.
In addition, the numeral below the square described in Fig. 6-5 ,-4 ... 5 expressions are for each value of the above-mentioned numbering m of each optical detecting unit 35 (i).
Each optical detecting unit 35 (i) can receive an independent folded light beam 32d (i) respectively, and produces electric signal S respectively R(i), its expression receives the amplitude of light.Control system 90 comprises that coupling is used to receive each detector output signal S R(i) each input end 95 (i).
In addition, according to the present invention, at least one has m=± m OPTThe photodetector unit be applicable to focus control.If can produce a component of signal or one group of signal that can obtain focus information, then optical detecting unit is applicable to focus control.Because focus control itself is known, and known focus control design itself can be applicable to the photodetector unit of focus control, and the present invention does not relate to the design that improves the photodetector unit, does not therefore discuss this design here in detail.Mention this photodetector unit and can comprise that a plurality of detector portion are just enough, wherein each detector portion receives the part of each light beam, and each detector portion produces the output signal of a correspondence, and control circuit is designed in a predetermined manner in conjunction with these output signals to obtain a focus error signal.
In the embodiment of this N=11, select m OPTEqual 4 (referring to Fig. 5 A), therefore, photodetector unit 35 (2) or photodetector unit 35 (10) are applicable to focus control at least.In the embodiment shown, photodetector unit 35 (2) and 35 (10) all is applicable to focus control.Fig. 6 shows that in these photodetector unit 35 (2) and 35 (10) each can both be subdivided into a plurality of (being four in this case) detector portion 35 (2) A, 35 (2) B, 35 (2) C, 35 (2) D, with 35 (10) A, 35 (10) B, 35 (10) C, 35 (10) D, each detector portion produces the output signal S of a correspondence R(2) A, S R(2) B, S R(2) C, S R(2) D, and S R(10) A, S R(10) B, S R(10) C, S R(10) D.
Control circuit 90 receives all above-mentioned signals.For focus control, control circuit 90 is designed to only use one group of signal S by a generation in described photodetector unit 35 (2) or 35 (10) R(2) A, S R(2) B, S R(2) C, S R(2) D or S R(10) A, S R(10) B, S R(10) C, S R(10) D.Also may be designed to use two groups of signals by control circuit 90, for example use the mean value of described signal according to following formula:
S RA＝(S R(2)A+S R(10)A)/2
S RB＝(S R(2)B+S R(10)B)/2
S RC＝(S R(2)C+S R(10)C)/2
S RD＝(S R(2)D+S R(10)D)/2
It will be apparent to those skilled in the art that the embodiment of being discussed above the invention is not restricted to, various deformation or modification in defined the present invention scope required for protection as claims are possible.
Hereinbefore, with reference to expression according to the block diagrams explaining of the functional part of device of the present invention the present invention.Be to be understood that and carry out one or more these functional blocks by hardware, wherein the function of this functional block is carried out by independent hardware element, but also can carry out one or more these functional blocks, so that the function of carrying out this functional block by the one or more program lines or the programmable device (for example microprocessor, microcontroller, data signal processor etc.) of computer program by software.

Claims (20)

1, be used to control the method for disc drive unit (1), this equipment comprises:
-be used for the optical system (30) of scanning disk (2), comprising:
-be suitable for producing the beam generated device (31) of a plurality of N bar light beams (32 (i));
-be used for described light beam (32 (i)) is focused on the device (33,34,37) of each focal beam spot (F (i));
-at least one is used for the adjustable element (34) of the described focal beam spot of axial dislocation (F (i));
Described method comprises step:
-to described adjustable element (34) calculating optimum setting (Z OPTIMUM), so that, promptly consider all light beams together generally for optical system (30), the non-focusing condition as far as possible little
2, according to the process of claim 1 wherein that described adjustable element (34) is the object lens that axially-displaceable is put.
3, according to the method for claim 1, wherein be defined as MAX (Δ z (i)) for the described non-focusing condition of optical system (30) generally, the axial distance between the ideal position of the physical location of i focal beam spot of Δ z (i) expression (F (i)) and i focal beam spot (F (i)) wherein, and wherein MAX (Δ z (i)) represents the maximal value of all Δ z (i) values.
4, according to the process of claim 1 wherein that described focal beam spot (F (i)) is located at position z 0In the focussing plane of locating to intersect (FP) with optical axis; Wherein N is an odd number;
And wherein the described the best for described adjustable element (34) is provided with (Z OPTIMUM) satisfy formula
Z OPTIMUM-z 0＝-(N-1) 2·d 2/(16R)
Wherein R represents the radius-of-curvature of the focussing plane (FP) near optical axis.
5, according to the process of claim 1 wherein that focal beam spot (F (i)) is located at position z 0In the focussing plane of locating to intersect (FP) with optical axis; Wherein N is an even number;
And wherein the described the best for described adjustable element (34) is provided with (Z OPTIMUM) satisfy formula
Z OPTIMUM-z 0＝-(N 2-2N+2)·d 2/(16R)
Wherein R represents the radius-of-curvature of the focussing plane (FP) near optical axis.
6, be substantially equal to the described best (Z of setting according to the process of claim 1 wherein that the position of adjustable element (34) is controlled as OPTIMUM).
7, according to the method for claim 1, described method further comprises step:
-calculating optimum light beam numbering (m OPT), when this particular beam is in correct focused condition, makes and promptly to consider all light beams 32 ((i)) together generally for optical system (30), the non-focusing condition as far as possible little.
8, according to the process of claim 1 wherein that N is the odd number greater than 3;
And wherein optimum laser beam is numbered (m OPT) satisfy formula
m OPT＝±INTEGERSQUARE{(N-1)/(2√2)}
Wherein function y=INTEGERSQUARE{x} is defined as integer y, its square y 2Near x 2
And wherein m=0 is corresponding to central light beam.
9, according to the process of claim 1 wherein N=3, and wherein optimum laser beam is numbered m OPT=0 or m wherein OPT=± 1.
10, according to the process of claim 1 wherein that N is the even number greater than 4;
And wherein optimum laser beam is numbered (m OPT) satisfy formula
m OPT＝±INTEGERROUND{N·(N-2)/8}
Wherein function z=INTEGERROUND{x} is defined as integer z, and z for z (z-1) is near x;
And wherein m=± 1 is corresponding to interior side beam.
11, according to the process of claim 1 wherein N=4, and optimum laser beam numbering m wherein OPT=± 1 or m wherein OPT=± 2.
12, according to the method for claim 1, described method further comprises step:
-from having optimum laser beam numbering (m=m OPTOr m=-m OPT) light beam receive reflected light;
-obtain focus error signal from this folded light beam;
-control the location of described adjustable element (34) according to this focus error signal.
13, according to the method for claim 1, described method further comprises:
-from having optimum laser beam numbering (m 1=m OPTAnd m 2=-m OPT) two light beams receive reflected light;
-obtain focus error signal, the contribution of average two light beams from these folded light beams;
-control the location of described adjustable element (34) according to this focus error signal.
14, disc drive unit (1), this equipment comprises:
-be used for the optical system (30) of scanning disk (2), comprising:
-be suitable for producing the beam generated device (31) of a plurality of N bar light beams (32 (i));
-described light beam (32 (i)) is focused on the device (33,34,37) of each focal beam spot (F (i));
-at least one is used for the adjustable element (34) of the described focal beam spot of axial dislocation (F (i));
-actuator system (50) comprises the may command focus actuator (52) that is used for the described adjustable element of axial dislocation (34);
-photodetector is arranged (35), comprises a plurality of detector cells (35 (i)), and the light beam (32 (i)) that each detector cell is arranged for from correspondence receives reflected light and is used to produce the electrical output signal (S that expression receives light R(i));
-control circuit (90), its signal input part (95 (i)) with coupling is to receive the electrical output signal (S of detector cell (35 (i)) RAnd be suitable for producing the focus control signal (S be used for focus actuator (52) (i)), CF);
Wherein control circuit is suitable for the described method of arbitrary claim among the enforcement of rights requirement 1-13.
15,, wherein have best numbering (35 (m=m according to the equipment of claim 14 OPT) or 35 (m=-m OPT)) detector cell be subdivided into a plurality of detector portion, each detector portion is used to produce corresponding detector portion output signal;
Wherein control circuit (90) is coupled the detector portion output signal that is used to receive described detector cell;
Wherein control circuit is suitable for handling the described detector portion output signal of described detector cell to obtain focus error signal;
And wherein control circuit is suitable for producing its focus control signal (S based on the focus error signal of such acquisition CF).
16,, wherein have best numbering (35 (m=m according to the equipment of claim 14 OPT) and 35 (m=-m OPT)) two detector cells all be subdivided into a plurality of detector portion, each detector portion is used to produce corresponding detector portion output signal;
Wherein control circuit (90) is coupled the detector portion output signal that is used to receive two described detector cells;
Wherein control circuit is suitable for handling the described detector portion output signal of described detector cell to obtain focus error signal, the respective contribution of average two described detector cells;
And wherein control circuit is suitable for producing its focus control signal (S based on the focus error signal of such acquisition CF).
17, according to the equipment of claim 15 or 16, wherein N is the odd number greater than 3;
And wherein best numbering (m OPT) satisfy formula
m OPT＝±INTEGERSQUARE{(N-1)/(2√2)}
Wherein function y=INTEGERSQUARE{x} is defined as integer y, its square y 2Near x 2
And wherein m=0 is corresponding to central light beam.
18, according to the equipment of claim 15 or 16, wherein N=3, and wherein best numbering m OPT=0 or m wherein OPT=± 1.
19, according to the equipment of claim 15 or 16, wherein N is the even number greater than 4;
And wherein best numbering (m OPT) satisfy formula:
m OPT＝±INTEGERROUND{N·(N-2)/8}
Wherein function z=INTEGERROUND{x} is defined as integer z, and z for it (z-1) is near x;
And wherein m=± 1 is corresponding to interior side beam.
20, according to the equipment of claim 15 or 16, wherein N=4, and wherein best numbering m OPT=± 1 or m wherein OPT=± 2.
CNA2005800238343A 2004-07-14 2005-07-11 Focus control in a multiple-beam disc drive Pending CN1985311A (en)

Applications Claiming Priority (2)

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EP04103357.2 2004-07-14

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JP (1) JP2008507075A (en)
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CN (1) CN1985311A (en)
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JP2008507075A (en) 2008-03-06
EP1769499A1 (en) 2007-04-04
ATE407425T1 (en) 2008-09-15
KR20070034098A (en) 2007-03-27
TW200617920A (en) 2006-06-01
US20080019237A1 (en) 2008-01-24
WO2006008694A1 (en) 2006-01-26
EP1769499B1 (en) 2008-09-03

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